A normal human heart pumping pattern is called a sinus rhythm, and is regulated by the body's biological pacemaker within the upper right chamber of the heart, which is commonly referred to as the right atrium. This natural pacemaker, which is generally referred to as the sinoatrial (SA) node, sends electrical signals to the right and left ventricular muscles in the lower chambers of the heart. The ventricular muscles then execute the pumping action under control of the SA node. The right ventricular muscle pumps blood to the lungs for oxygenation, and the left ventricular muscle pumps the oxygenated blood to various parts of the body.
In certain circumstances, the normal or sinus heartbeat rhythm may be adversely affected as a result of some type of malfunction in the heart's electrical control system. When this type of malfunction occurs, an irregular heartbeat may result, causing the ventricular muscles to pump ineffectively, thus reducing the amount of blood pumped to the body. This irregular heartbeat is generally referred to as an arrhythmia and can lead to Sudden Cardiac Arrest (SCA).
It is estimated that approximately two hundred and twenty-five thousand (225,000) deaths per year are attributable to SCA. A particularly serious type of SCA is known as Ventricular Fibrillation (VF), which is a malfunction characterized by rapid, uncoordinated cardiac movements replacing the normal contractions of the ventricular muscles. In this event, the ventricular muscles are not able to pump blood out of the heart, and there is no initiation of a heartbeat. VF rarely terminates spontaneously, and is therefore a leading cause of sudden cardiac death. The unpredictability of VF and other irregular heart beat conditions exacerbates the problem, and emphasizes the need for early therapeutic intervention to prevent the loss of life.
Defibrillators are devices for providing life-saving electrical shock therapy to persons experiencing an irregular heat beat, such as VF. A defibrillator provides an electrical shock to the heart, in order to convert the irregular heart beat to a normal sinus rhythm One type of defibrillator, an implantable cardioverter defibrillator (ICD), is surgically implanted in patients who are considered likely to need electrical shock therapy, precluding the necessity of constant monitoring by medical personnel.
Another commonly used type of defibrillator is the external defibrillator, which sends electrical shock pulses to the patient's heart through external electrodes applied to the patient's chest. External defibrillators may be manually operated, as are typically used in hospitals by medical personnel or may be semi-automatic, semi-automated, fully automatic, or fully automated devices, where they can be used in any location where an unanticipated need may occur. An automatic external defibrillator is commonly referred to as an AED.
It is well known that time is an important factor in the successful application of electrical shock therapy. The survival rate of persons suffering from ventricular fibrillation decreases by about ten percent (10%) for each minute the administration of a defibrillation shock is delayed. It is therefore desirable to minimize the time duration between powering up an external defibrillator and administering the electrical shock therapy to the patient. It is also estimated that the rate of survival for SCA victims averages less than two percent (2%) when defibrillation is delayed ten (10) minutes or more.
In a typical usage of a defibrillator, the defibrillator electrodes are attached to the patient prior to delivery of a defibrillation shock. The defibrillator can also monitor the patient's condition and physiological parameters. This data can be measured and analyzed, and then an appropriate therapy determined. If a shock is recommended, the defibrillator charges to an appropriate level and applies the shock therapy in a desired format. One or more of these activities can be done by medical/emergency personnel, as in the case of manual defibrillators, or by an automatic or automated process, as in the case of automatic, semi-automatic, automated and semi-automated defibrillators. These actions, while necessary, can be disadvantageously time-consuming, and can delay the administration of the shock therapy.
Additionally, some defibrillators integrate cardiopulmonary resuscitation (CPR) instructions along with shock treatment. CPR is a combination of techniques including artificial respiration (rescue breathing) and artificial circulation (chest compression). One purpose of CPR is to provide oxygenated blood through the body, and to the brain, in those patients where a prolonged loss of circulation places the patient at risk. For example after a period of time without restored circulation, typically within four (4) to six (6) minutes, cells in the human brain can begin to be damaged by lack of oxygen. In some cases, shock therapy does not immediately restore a normal heart rhythm; several shocks may be required. In other cases, CPR should be administered prior to any defibrillation therapy. Thus, for some patients the appropriate treatment calls for a combination of shock therapy and CPR while other cases may call for shock therapy first.
Many defibrillators also include a CPR protocol. A CPR protocol typically uses voice prompts and/or a form of interactive display that guides a user in when to apply CPR methods and shock therapy. A CPR-first protocol has been proposed for use with some defibrillators. Under this protocol, the defibrillator is configured to prompt CPR as the first type of therapy to be given to a patient. In such a device the defibrillator may also include ECG (electrocardiogram) capability in order to monitor patient conditions. One example of an external defibrillator with CPR prompts is described in U.S. Pat. No. 6,356,785. Another example is described in U.S. Pat. No. 6,334,070. The CPR protocol includes prompts which indicate when CPR should be applied. The prompt may be in the form of a visual/graphical display, an audio display, or some other form of communication.
Referring now to FIG. 1 there is illustrated a flow chart that describes a CPR-first defibrillator protocol. A usage of the defibrillator begins when it is brought to the scene of an emergency and activated 2. The first action 4 of the machine is to instruct a CPR therapy to the user. After issuing the CPR instructions, and any attendant routine of queries and responses within the CPR protocol, the machine then performs an analysis 6 of the patient's ECG to determine if it is advisable to deliver a defibrillating shock 8. This analysis is referred to as “shock analysis” in this document. It is noted that in this system a CPR-first instruction is the automatic, default action of the device.
While it is advantageous to integrate CPR and shock therapy, there are instances in which CPR first, prior to shock therapy, is not the appropriate patient treatment. In these cases, shock therapy should be administered first, and any delay in doing so is potentially adverse to the patient. Nevertheless, in those systems that have a default CPR-first protocol, it is required that a user first pass through the CPR prompts in order to reach the shock treatment protocol.
Hence there exists a need for an improved defibrillator and an improved method for operating a defibrillator. Namely, there is a need for a defibrillator, and especially an external defibrillator, that addresses one of more of the above-noted drawbacks and limitations. It would be desired to provide a defibrillator and a control system thereof that reduces the inherent time delays associated with shock administration in external defibrillators. In addition, it would be desired to provide a defibrillator that includes convenient interactive features so that output and input can be quickly received and supplied by a human operator/user. Finally, it would be desired to provide a defibrillator that, by virtue of the foregoing, offers an improved level of response and patient treatment. The present invention addresses one or more of these needs.